Callout Mediator

The Callout mediator performs a blocking external service invocation during mediation.

As the Callout mediator performs a blocking call, it cannot use the default non-blocking HTTP/S transports based on Java NIO. Instead, it defaults to using <ESB_HOME>/repository/conf/axis2/axis2_blocking_client.xml as the Axis2 configuration, and <ESB_HOME>/repository/deployment/client as the client repository unless these are specified separately.

The Call mediator leverages the non-blocking transports for much greater performance than the Callout mediator, so you should use the Call mediator in most cases. However, the Callout mediator is recommended in situations where you need to execute the mediation flow in a single thread.

Setup

Enabling mutual SSL

Since the Callout mediator is run based on the configuration of the axis2_blocking_client.xml file, its default https transport sender is org.apache.axis2.transport.http.CommonsHTTPTransportSender. Therefore, the Callout mediator does not have access to the required key store to handle mutual SSL. To enable the Callout mediator to handle mutual SSL, the following JVM settings should be added to the <ESB_HOME>/bin/wso2server.sh file.

 -Djavax.net.ssl.keyStore="$CARBON_HOME/repository/resources/security/wso2carbon.jks" \
 -Djavax.net.ssl.keyStorePassword="wso2carbon" \
 -Djavax.net.ssl.keyPassword="wso2carbon" \

Disabling chunking

The Callout mediator is not affected by the DISABLE_CHUNKING property. Instead, you can disable chunking for the Callout mediator by setting the Transfer-Encoding parameter to ‘none’ in CommonsHTTPTransportSender of axis2_blocking_client.xml as follows:

<parameter name="Transfer-Encoding">none</parameter>

For example:

<transportSender name="http"
                 class="org.apache.axis2.transport.http.CommonsHTTPTransportSender">
        <parameter name="PROTOCOL">HTTP/1.1</parameter>
        <parameter name="Transfer-Encoding">none</parameter>
        <parameter name="cacheHttpClient">true</parameter>
        <parameter name="defaultMaxConnectionsPerHost">200</parameter>
</transportSender>

This will disable chunking for all Callout mediators present in the ESB server.

If you want to disable chunking for only a single Callout mediator instance, create a new axis2.xml file by copying the axis2_blocking_client.xml file, set the Transfer-Encoding parameter as shown, and then configure that Callout mediator to use this new axis2.xml file as described below.

Syntax

<callout [serviceURL="string"] [action="string"] [initAxis2ClientOptions="true|false"] [endpointKey="string"]>
      <configuration [axis2xml="string"] [repository="string"]/>?
      <source xpath="expression" | key="string" | type="envelope"/>
      <target xpath="expression" | key="string"/>
      <enableSec policy="string" | outboundPolicy="String" | inboundPolicy="String" />?
</callout>

UI configuration

To add the Callout mediator to a sequence, click Add Child at the point in the sequence tree where you want to add the mediator, and then choose Advanced -> Callout.

The parameters available for configuring the Callout mediator are as follows.

Parameter Name	Description
Specify As	This parameter determines whether the target external service should be configured by using either a `serviceURL` attribute or an `endpointKey` attribute. URL: Select URL if you want to call the external service by specifying its URL in the Call mediator configuration. Address Endpoint: Selected Address Endpoint if you want to call the external service via an Endpoint which is already saved in the Registry. This option should be selected if you want to make use of the WSO2 functionality related to endpoints such as format conversions, security etc. Note that only Leaf endpoint types (i.e. `Address`, `WSDL`, `Default` and `Http`) are supported for the Callout mediator. If neither a URL or an address endpoint is specified, the `To` header on the request is used as the target endpoint.
URL	If you selected URL for the Specify As parameter, use this parameter to enter the URL of the external service that you want to call. This URL will be used as the End Point Reference (EPR) of the external service.
Address Endpoint	If you selected Address Endpoint for the Specify As parameter, use this parameter to enter key to access the endpoint that should be used to call the external service. Click Configuration Registry or Governance Registry as relevant to select the required endpoint from the resource tree.
Action	The SOAP action which should be appended to the service call.
Axis2 Repository	The path to Axis2 client repository where the services and modules are located. The purpose of this parameter is to make the Callout mediator initialize with the required client repository.
Axis2 XML	The path to the location of the Axis2 XML configuration file. The purpose of this parameter is to make the Callout mediator initialize with the relevant Axis2 configurations, such as if you want to disable chunking just for this Callout mediator instance as described above.
Source	This parameter defines the payload for the request. It can be defined using one of the following options. XPath - This option allows you to specify an expression that defines the location in the message. Tip You can click NameSpaces to add namespaces if you are providing an expression. Then the Namespace Editor panel would appear where you can provide any number of namespace prefixes and URLs used in the XPath expression. Property - This option allows you to specify the payload for a request via a property included in the mediation flow. Envelope - This option allows you to select the entire envelope which is available in the message flow as the source.
Target	The node or the property of the request message to which the payload (resulting from the value specified for the Source parameter) would be attached. The target can be specified using one of the following options. XPath - This option allows you to specify an expression that defines the location in the message. Tip You can click NameSpaces to add namespaces if you are providing an expression. Then the Namespace Editor panel would appear where you can provide any number of namespace prefixes and URLs used in the XPath expression. Property - This option allows you to specify a property included in the mediation flow.
WS-Security	If this check box is selected, WS-Security is enabled for the Callout mediator. This section would expand as shown below when you select this check box.
Specify as Inbound and Outbound Policies	If this check box is selected, you can define separate security policies for the inbound and outbound messages (flows). This is done by entering the required policy keys in the Outbound Policy Key and Inbound Policy Key parameters which are displayed as follows when this check box is selected. You can click Configuration Registry or Governance Registry to select a security policy saved in the Registry from the resource tree.
Policy Key	If the Specify as Inbound and Outbound Policies check box is not selected, this parameter is used to enter a key to access a security policy which will be applied to both inbound and outbound messages. You can click Configuration Registry or Governance Registry to select a security policy saved in the Registry from the resource tree.

You can also configure the mediator using XML by clicking switch to source view in the Mediator window.

Example

<callout serviceURL="http://localhost:9000/services/SimpleStockQuoteService"
         action="urn:getQuote">
    <source xmlns:s11="http://schemas.xmlsoap.org/soap/envelope/"
            xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
            xpath="s11:Body/child::*[fn:position()=1] | s12:Body/child::*[fn:position()=1]"/>
    <target xmlns:s11="http://schemas.xmlsoap.org/soap/envelope/"
            xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
            xpath="s11:Body/child::*[fn:position()=1] | s12:Body/child::*[fn:position()=1]"/>
</callout>

In this example, the Callout Mediator does the direct service invocation to the StockQuoteService using the client request, gets the response, and sets the response as the first child of the SOAP message body. You can then use the Send Mediator to send the message back to the client.